Published: 6 March, 2003

Not Your Grandparents Crystal Radio

Where are the crystals in the crystal radio?

What a swell question. First, for folks who have never met one, a crystal radio is a beautifully simple radio that picks up local AM stations readily without using a battery or plugging it into a wall power outlet (I'm listening to the Beatles from WTKO on one as I write this). The crystal that these radios are named after is actually a pair of special materials that touch each other. Together they make a crystal diode which sits smack in the middle of the radio. It's the job of the crystal diode to help pull the sound wave (in this case music) off the radio wave that got it from the radio station to the wire in my back yard that serves as an antenna.

It is a pretty clever idea to put sound on a radio wave since it goes out over a much greater distance than the music would by itself alone.

In our grandfather's day a crystal diode used a shiny chunk of a mineral called galena. The galena piece really looked like a gem, so "crystal radio" was a pretty good name for one of these sets. The other half of Grandfather's diode was a small metal wire that he used to touch the galena. Nowadays we say that the metal is also a crystal in the modern sense (a bunch of atoms stacked together like bricks in a wall).

My radio uses a tiny piece of another mineral, germanium, also touched by a fine metal wire. This crystal diode is held together in a glass tube only about 1/4 inch long. Like a lot of neat electronics we enjoy today this part is really small in size compared to Grandfather's crystal. But let's not forget who taught us to how to make crystal radios in the first place.